## page was renamed from ReproducibleBuilds/TimestampInGzipHeaders
`gzip` stores a timestamp by default in its header.

This prevents build to be reproducible and capture an uninteresting details.

Packages known to be affected:

 * [[https://reproducible.debian.net/userContent/issues/timestamps_in_gzip_headers_issue.html|Identified as such]]
 * [[http://lintian.debian.org/tags/gzip-file-is-not-multi-arch-same-safe.html|All packages with Lintian tag gzip-file-is-not-multi-arch-same-safe]]

= Detection =

[[attachment:br.ispell_3.0~beta4-17.debbindiff.html|Example debbindiff output]].

`file` will display the timestamp if there's one.

= Work-around =

DebianPts:strip-nondeterminism will take care of normalizing gzip'ed files.

= Solution =

Pass `-n` or `--no-name` option to `gzip`.

[[https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=0002-Stop-recording-current-time-when-using-gzip.patch;att=2;bug=774347|Example patch]]

Quoting the manpage:
{{{
The environment variable GZIP can hold a set of default options for gzip.
}}}

It can be used for applications like `tar`.

= Prevention =

Lintian tag: [[https://lintian.debian.org/tags/package-contains-timestamped-gzip.html|package-contains-timestamped-gzip]]

Ideally, we would set it as a default environment variable at the
`dpkg-buildpackage` level. Unfortunately, this was experimented previously with
CFLAGS (and the likes) similarily exported and this made many maintainers grumpy. *sigh*